A known autostereoscopic display device comprises a two-dimensional liquid crystal display panel having a row and column array of display pixels acting as an image forming means to produce a display. An array of elongated lenses extending parallel to one another overlies the display pixel array and acts as a view forming means. These are known as “lenticular lenses”. Outputs from the display pixels are projected through these lenticular lenses, which function to modify the directions of the outputs.
The lenticular lenses are provided as a sheet of lens elements, each of which comprises an elongate semi-cylindrical lens element. The lenticular lenses extend in the column direction of the display panel, with each lenticular lens overlying a respective group of two or more adjacent columns of display sub-pixels.
Each lenticular lens can be associated with two columns of display sub-pixels to enable a user to observe a single stereoscopic image. A sub-pixel is the smallest addressable pixel structure and has only one single color. Generally a group of sub-pixels, which together can generate all desired colors, is denoted as pixel. Instead, each lenticular lens can be associated with a group of three or more adjacent display sub-pixels in the row direction. Corresponding columns of display sub-pixels in each group are arranged appropriately to provide a vertical slice from a respective two dimensional sub-image. As a user's head is moved from left to right a series of successive, different, stereoscopic views are observed creating, for example, a look-around impression.
The above described autostereoscopic display device produces a display having good levels of brightness. However, one problem associated with the device is that the views projected by the lenticular sheet are separated by dark zones caused by “imaging” of the non-emitting black matrix which typically defines the display sub-pixel array. These dark zones are readily observed by a user as brightness non-uniformities in the form of dark vertical bands spaced across the display. The bands move across the display as the user moves from left to right and the pitch of the bands changes as the user moves towards or away from the display.
This banding problem arises in particular because current autostereoscopic displays employ a matrix of pixels that are square in shape. In order to generate images in color, the pixels are divided into sub-pixels. Traditionally, each pixel is divided into 3 sub-pixels, transmitting or emitting red (R), green (G) and blue (B) light, respectively. Sub-pixels of equal color are typically arranged in columns. This is the structure of the most standard RGB panel, with so-called RGB-stripes. Each sub-pixel is surrounded by the black matrix. It is the regularity of the pixel grid (and color distribution) combined with the magnification of the lenticular lens which causes the banding problem.
Another problem is that vertically aligned lenses result in a reduction in resolution in the horizontal direction only, while the resolution in the vertical direction is not altered.
Both of these issues can be at least partly addressed by the well-known technique of slanting the lenticular lenses at an acute angle relative to the column direction of the display pixel array, for example as described in U.S. Pat. No. 6,064,424A1. The use of slanted lenses is thus recognised as an essential feature to produce different views with near constant brightness, and a good RGB distribution behind the lenses. The slanting of the lenses distributes the resolution loss between horizontal and vertical direction.
However, the slanted lens solution has some disadvantages: a slanted lens may be more difficult to manufacture, particularly when a switchable solution is desired and, more importantly, the 3D pixels are non-rectangular, and are not arranged along row and column directions. This introduces some aliasing for horizontal and vertical lines, especially when used in text and computer graphics.
WO2010/070564 discloses an arrangement in which the lens pitch and lens slant are selected in such a way as to provide an improved pixel layout in the views created by the lenticular array, in terms of spacing of color sub-pixels, and color uniformity.
The present invention relates specifically to autostereoscopic displays in which non-slanted lenticular lenses, barriers or a non-slanted microlens array are used. However, although it is considered an important advantage of the invention that a display with reduced banding can be made without the need for slanting the lens (or barrier), it is not excluded that in addition the lens can also be slanted. It is known that an equivalent to slanting the lenses is to stagger the pixel rows so that the columns effectively have a stepped slant. This is disclosed for example in WO 2012/176102.
Although the solution disclosed in WO 2012/176102 will have less banding problems, the shape of the sub-pixels can still be perceived as banding. The staggered layout also gives rise to a 3D sub-pixel shape which depends on the type of 2D pixel grid, and may be not ideal.
Another important aspect is a relationship between the display sub-pixel sizes and shapes and the way the 2D sub-pixels are mapped to sub-pixels of the 3D images.
For example the use of a standard RGB panel and slanted lenticulars with certain relation between the lens pitch and slant result in the 3D pixels of the views ordered on a hexagonal grid (so-called delta-nabla pattern), which creates problems in rendering images with sharp horizontal and vertical edges without aliasing, especially text.
It is an aim of the current invention to provide new pixel layouts, which in combination with non-slanted view forming arrangements will create a 3D display with high quality, with reduced amount of banding, smooth transitions between the views, and in particular by taking into account the mapping of 2D sub-pixel sizes and shapes, and the resulting 3D image sub-pixels, which are preferably arranged along the rows and column directions with good and uniform color distribution.